The HIV-1 epidemic has resulted in ~5 million new infections in 2004 for a total of 40 million people living with HIV/AIDS. A vaccine that can protect against virus infection is a major public health need. However, the extensive sequence diversity of HIV-1 represents a major impediment to vaccine research. Some 9 clades (genetic subtypes) have been defined, along with numerous circulating recombinant forms. Certain clades of virus have become predominantly localized to specific geographical areas of the world, for example: clade A in East Africa; clade B in North and South America as well as Europe; and clade C in South Africa, India and parts of China. The populations living in these areas display extensive polymorphism of certain genes of the immune system, called HLA. The various HLA types exert an important influence on the sequences of circulating HIV-1. We hypothesize that the current sequences of circulating viruses have evolved, at least in part, due to immune pressure and that the dominant clades in certain geographic areas are lacking certain epitopes that would otherwise be involved in an effective prophylactic immune response to the virus. Our hypothesis suggests that an appropriate combination of sequences drawn from different clades could result in HIV-1 proteins that are more immunogenic than the existing wild-type sequences. In this Phase I SBIR project, we will carry out multigene in vitro DMA recombination using consensus env genes from clades A, B, C, and Group M to create genes expressing chimeric viral envelope (Env) proteins. The expressed proteins will be prescreened in an unbiased way, based on binding to CD4, to identify Env proteins that are efficiently secreted and well-folded. In a subsequent Phase II SBIR project, we will perform immunization studies to evaluate the ability of each protein to induce virus-neutralizing antibodies. The Specific Aims of this Phase I SBIR proposal are summarized below.-Specific Aim #1: Create libraries of Env variants using in vitro DNA recombination; -Specfic Aim #2: Isolate thousands of individual clones from libraries of Env variants; -Specific Aim #3: Select secreted Env variants that bind CD4. [unreadable] [unreadable] [unreadable]